Even though the automotive industry has over the years, if for no other reason than seeking competitive advantages, continually exerted efforts to increase the fuel economy of automotive engines, the gains continually realized thereby have been deemed by various levels of governments to be insufficient. Further, such levels of government have also imposed regulations specifying the maximum permissible amounts of carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NO.sub.x) which may be emitted by the engine exhaust gases into the atmosphere.
Unfortunately, the available technology employable in attempting to attain increases in engine fuel economy is, generally, contrary to that technology employable in attempting to meet the governmentally imposed standards on exhaust emissions.
For example, the prior art, in trying to meet the standards for NO.sub.x emissions, has employed a system of exhaust gas recirculation whereby at least a portion of the exhaust gas is re-introduced into the cylinder combustion chamber to thereby lower the combustion temperature therein and consequently reduce the formation of NO.sub.x.
The prior art has also proposed the use of engine crankcase recirculation means whereby the vapors which might otherwise become vented to the atmosphere are introduced into the engine combustion chambers for burning.
The prior art has also proposed the use of fuel metering means which are effective for metering a relatively overly-rich (in terms of fuel) fuel-air mixture to the engine combustion chamber means as to thereby reduce the creation of NO.sub.x within the combustion chamber. The use of such overly rich fuel-air mixtures results in a substantial increase in CO and HC in the engine exhaust, which, in turn, requires the supplying of additional oxygen, as by an associated air pump, to such engine exhaust in order to complete the oxidation of the CO and HC prior to its delivery into the atmosphere.
The prior art has also heretofore proposed retarding of the engine ignition timing as a further means for reducing the creation of NO.sub.x. Also, lower engine compression ratios have been employed in order to lower the resulting combustion temperature within the engine combustion chamber and thereby reduce the creation of NO.sub.x.
The prior art has also proposed the use of fuel metering injection means instead of the usually-employed carbureting apparatus and, under superatmospheric pressure, injecting the fuel into either the engine intake manifold or directly into the cylinders of a piston type internal combustion engine. Such fuel injection system, besides being costly, have not proven to be generally successful in that the system is required to provide metered fuel flow over a very wide range of metered fuel flows. Generally, those injection system which are very accurate at one end of the required range of metered fuel flows, are relatively inaccurate at the opposite end of that same range of metered fuel flows. Also, those injection systems which are made to be accurate in the mid-portion of the required range of metered fuel flows are usually relatively inaccurate at both ends of that same range. The use of feedback means for altering the metering characteristics of a particular fuel injection system have not solved the problem because the problem usually is intertwined with such factors as: effective aperture area of the injector nozzle; comparative movement required by the associated nozzle pintle or valving member; inertia of the nozzle valving member and nozzle "cracking" pressure (that being the pressure at which the nozzle opens). As should be apparent, the smaller the rate of metered fuel flow desired, the greater becomes the influence of such factors thereon.
It is anticipated that the said various levels of government will establish even more stringent exhaust emission limits and even higher standards of fuel economy.
The prior art, in view of such anticipated requirements with respect to NO.sub.x, has suggested the employment of a "three-way" catalyst, in a single bed, within the stream of exhaust gases as a means of attaining such anticipated exhaust emission limits. Generally, a "three-way" catalyst (as opposed to the "two-way" catalyst system also well known in the prior art) is a single catalyst, or catalyst mixture, which catalyzes the oxidation of hydrocarbons and carbon monoxide and also the reduction of oxides of nitrogen. It has been discovered that a difficulty with such a "three-way" catalyst system is that if the fuel metering is too rich (in terms of fuel), the NO.sub.x will be reduced effectively, but the oxidation of CO will be incomplete. On the other hand, if the fuel metering is too lean, the CO will be effectively oxidized but the reduction of NO.sub.x will be incomplete. Obviously, in order to make such a "three-way" catalyst system operative, it is necessary to have very accurate control over the fuel metering function of associated fuel metering supply means feeding the engine. As hereinafter described, the prior art has suggested the use of fuel injection means with associated feedback means (responsive to selected indicia of engine operating conditions and parameters) intended to continuously alter or modify the metering charactertistics of the fuel injection means. However, at least to the extent hereinafter indicated, such fuel injection systems have not proven to be successful.
It has also heretofore been proposed to employ fuel metering means, of a carbureting type, with closed loop feedback means responsive to the presence of selected constituents comprising the engine exhaust gases. Such closed loop feedback means were employed to modify the action of a main metering rod of a main fuel metering system of a carburetor. However, tests and experience have indicated that such a prior art carburetor with such a related closed loop feedback means could not provide the degree of accuracy required in the metering of fuel to an associated engine as to assure meeting, for example, the said anticipated emission and fuel economy standards.
Also, heretofore, the prior art has proposed an arrangement whereby a carburetor, having an induction passage therethrough with a venturi therein and a main fuel discharge nozzle situated generally within the venturi, has a main fuel metering system communicating generally between a fuel reservoir and the main fuel discharge nozzle along with an idle fuel metering system communicating generally between a fuel reservoir and said induction passage at a location generally in close proximity to an edge of a variably openable throttle valve situated in the induction passage downstream of the main fuel discharge nozzle. Modulating valving means are provided to controllably alter the rate of metered fuel flow through each of the main and idle fuel metering systems in response to control signals generated as a consequence of selected indicia of engine operation. Such indicia comprised engine exhaust gas constituent responsive means for sensing the relative percentage of selected exhaust gas constituents and producing control signals in response thereto. Also, electronic computer means are usually provided for processing all of the control signals and, in response thereto, producing an output signal or signals effective for controlling the modulating valving means.
In the main, such prior art systems can not be readily adapted to all engines and vehicles especially where such engines and/or vehicles were manufactured prior to the commercial availability of such prior art fuel metering systems.
Accordingly, the invention as herein disclosed is primarily directed to the provision of a fuel metering system which can be readily adapted to carburetors constructed in accordance with the prior art and already being employed on vehicle engines and which, further, enables the vehicle operator a certain degree of control thereover in order to be able to select, for example, the rate of metered fuel flow to the engine in order to obtain maximum fuel economy for whatever engine demands are being then experienced.